The invention relates to a vehicle door.
A vehicle door of this type has an inner door panel, an outer door panel with an inner surface facing the inner door panel, and a loudspeaker which is arranged on the inner door panel, is spaced apart from the outer door panel and is intended for generating acoustic sound waves.
In the case of a vehicle door of this type known, for example, from DE 196 22 310 A1 loudspeaker is arranged on a unit carrier of a door module and is fastened to an inner door panel via the unit carrier of the door module. The loudspeaker which is designed as a conical loudspeaker projects into a wet chamber of the vehicle door, which wet chamber is formed between the inner door panel and the outer door panel, and, during operation, radiates acoustic sound waves both forward in the direction of a vehicle interior and rearward in the direction of the outer door panel.
In vehicle doors known nowadays, conical loudspeakers are frequently used for transmitting music within a frequency range of between 20 Hz and 10 kHz.
Such loudspeakers are mounted, for example, on a door module, on an inner door panel or on an inner door lining. A vehicle door can have a single loudspeaker or else a plurality of loudspeakers.
During the operation of a conical loudspeaker, a diaphragm is oscillated in order to generate airborne sound waves. Said sound waves propagate as airborne sound, wherein the sound waves are firstly radiated into the vehicle interior and secondly into the inner door region. Structure-borne sound generated by the loudspeaker can likewise also be coupled via the loudspeaker connection into the surrounding structure, for example the vehicle door. This can lead to an excitation of the structure of the vehicle door, which can then itself lead to a further excitation of the loudspeaker. The surrounding structure is further excited via the change in compression of the air volume located in the door by means of the loudspeaker which can then again excite the surrounding structure (vehicle door, for example inner door panel, outer door panel) to oscillate and therefore, in turn, leads to an airborne sound radiation of the structure. If said excitation of the structure has a phase displacement of between 0° and 180° with respect to the deflection of the loudspeaker, this may contribute to undesirable amplifying or extinguishing of the sound event and may cause negative fading, booming or reverberating and also an increase in the distortion factor (distortion) of the loudspeaker tone. Similarly, fading, blurring or booming of the loudspeaker tone may occur due to the formation of stationary waves in resonant structures or due to the excitation of structure-borne sound and the associated generation of secondary airborne sound because of oscillations and vibrations of components.
In order to avoid such disadvantageous effects on the acoustics, the use of an absorbing film or an absorbing fleece or a heavy film in or on door structures is known from the prior art. In addition, a dosed air volume can be provided for a loudspeaker. However, these measures have the disadvantage of possibly bringing about high costs and an increased weight and also a greater construction space in or on the vehicle door.
The radiation of sound waves in the direction of the outer door panel may also lead to an excitation of structure-borne sound of the outer door panel. Such an excitation of structure-borne sound takes place in particular if radiated sound waves strike perpendicularly against the outer door panel and, as a result, can advantageously be coupled into the structure of the outer door panel. Similarly, by direct acoustic irradiation of the outer door panel (direct sound strikes from the rear side of the loudspeaker via a free airborne sound path against the wet chamber side of the outer door panel and wet chamber of the door), the absorption of ultrasonic transmissions is determined only by the material, the structural properties of the outer door panel and the acoustic tightness of the wet chamber of the door toward the outer side of the vehicle. Said sound paths are bidirectional, and therefore sound—for example, speech which is radiated by the loudspeaker—can be perceived outside the vehicle. Furthermore, noises from outside the vehicle (tire noise, wind noises, driving noises . . . ) can pass via said sound paths into the passenger compartment and cause a deterioration in the interior noise level.
Precisely because of the extensive, lightweight structural composition of the outer door panels, the excitation by means of air and structure-borne sound produces a weak point here. This can lead, for example, to sound waves also being radiated outwards, i.e. into the exterior space outside the vehicle, and therefore sound waves generated by the loudspeaker are perceptible outside the vehicle, which may lead, for example, if the loudspeaker is used within the scope of a hands free telephone system, to telephone conversations being able to be heard outside the vehicle.